In recent years, color cathode ray tubes of the so-called flat face type or flat panel type are widely employed in television receiver sets and personal computer monitors. From a viewpoint of manufacturability and manufacturing cost, such flat panel type color cathode ray tubes are generally designed so that the outer surface of a display panel is formed into a substantially flat plane through increase of a radius of curvature (equivalent radius of curvature) thereof while forming on an inner panel surface a phosphor screen into a curved plane having a relatively small radius of curvature (equivalent radius of curvature) that is as small as possible not to spoil the flatness of display images. Due to this panel design, a peripheral portion of such panel is greater in thickness than a central portion thereof, which leads to the risk of multi-reflection of externally incident rays of light at the thick panel peripheral portion resulting in a degradation of quality of display images.
See FIG. 36, which is a diagram for explanation of an image quality degradation occurring when external light rays are reflected off at a panel of the flat panel color cathode ray tube. In FIG. 36, reference numeral xe2x80x9c1xe2x80x9d is used to designate a panel; 1a denotes a display screen section of the panel; 1b indicates a skirt section; 1c is a non-glare anti-static layer; line segment Zxe2x80x94Z shows a tube phosphor screen. As shown in FIG. 36, externally incident light rays Li are reflected off at an outer panel surface while at the same time behaving to reflect at an inner panel face to thereby outgo as reflected light Lr from the outer panel face, which would result in a decrease in viewability of picture images as visually displayed on the panel screen. Furthermore, the thick panel peripheral portion might also experience occurrence of multireflection in association with inner face reflection, which results in overlapping or xe2x80x9csuperpositionxe2x80x9d of multiple reflection image components onto a display image, thereby further reducing the viewability. It should be noted that although the discussion in conjunction with FIG. 36 was done while neglecting any possible influence of reflection on the outer panel face, such outer face reflection will hardly be precluded completely even when employing the nonglare antistatic layer 1c. 
A cathode ray tube with an optical selection/absorption layer provided between the inner panel face and phosphor screen has been disclosed in Japanese Patent Application Laid-Open Hei 4-345737/1992. The optical select/absorb layer as taught from this Japanese document is comprised of a mixture of more than two materials including organic or inorganic pigment or dye materials, wherein these pigment/dye materials are in the form of fine powdery grains or particles with a grain size of 1.0 micrometer (xcexcm) or less and also with two or more maximal spectral absorption peaks while forming on the outer panel face a mixture layer of a conductive material and a binder, or a single-layered antireflection layer that is lower in refractivity than a glass panel, or alternatively a multilayer antireflection film including two to four layers of different refractivities, or still alternatively a film with conductive particles made of ATO or ITO or else mixed into this multilayered antireflection film.
Another cathode ray tube is disclosed in Japanese Patent Application Laid-Open Hei 5-182604/1993, wherein in order to let its panel be uniform in optical transmissivity, a chosen coloring agent is mixed into a silica binder and is then spray-coated on an outer panel surface with the resultant coat density being variable so that a density value is high at a central portion and low at a peripheral portion; then, a conductive agent with no coloring agents added thereto is spray coated thereon to form a convex-concave surface configuration having its glossiness (gloss value) that is adjustable with a change in amount of ethylene glycol being added to a coating liquid used.
A color cathode ray tube is disclosed in U.S. Pat. No. 4,815,821, wherein the cathode ray tube includes a glass panel having on its inner surface a first transparent layer that is higher in refractivity than the panel glass, a black matrix (BM) formed thereon, and a second transparent layer overlying the black matrix to have reflectivity less than that of the first transparent layer, and wherein the refractivity of the first transparent layer is designed to fall within a range of 1.7 to 2.0 while letting each transparent layer be set at a quarter of the wavelength of visible light.
With flat panel color cathode ray tubes, it is required to lessen the radius of curvature of an inner panel surface to the extent that the lack of flatness is avoided when viewing on-screen display images by human eyes, thereby offering increased manufacturability and enhanced surface flatness of a tube bulb (evacuated envelop). As currently available color cathode ray tubes are typically designed to add a significant difference in radius of curvature to the panel""s inner surface and outer face in the way discussed above, the resulting plate thickness becomes greater at the periphery than at the center part thereof, which in turn results in occurrence of a problem that those display images at the panel periphery are made darker than an image being displayed at the center of such panel.
One prior known approach to reducing a difference in brightness or luminance intensity between the panel center and periphery is to employ a panel made of certain glass materials with increased optical transmissivities. Unfortunately this approach is encountered with problems which follow: the higher the optical transmissivity, the lower the contrast of display images; and, the operability of letting a glass material per se absorb for attenuation multireflection light rays at the panel""s inner and outer surfaces might likewise decrease resulting in a decrease in color purity.
Furthermore, in addition to improving the display image quality, it is also a must for color cathode ray tubes to meet the strict need for satisfying ergonomics design requirements including, but not limited to, preclusion of extraneous electromagnetic radiation and external attendant light prevention.
The present invention is to provide a flat panel color cathode ray tube excellent in panel face flatness and image contrast plus extended color reproduction range. To this end, the color cathode ray tube in accordance with this invention is specifically arranged to employ an inside light absorption layer containing therein inorganic pigment at a selected portion lying adjacent to a panel than a light absorption matrix (black matrix) on an inner panel surface or adversely providing an inside light absorption layer containing such inorganic pigment on or over the light absorption matrix (on an electron gun assembly side) to thereby suppress unwanted creation of multireflection on both the inner panel surface and outer surface, thus correcting or compensating for any possible difference in light absorption amount which can occur due to the presence of a plate thickness difference between a central portion and a peripheral portion of the panel. Another principal concept of the invention lies in forming on the outer panel surface an outside light absorption layer which consists essentially of a conductive micro-particle layer that offers light absorbability by itself and a low refractivity layer overlying this microparticle layer with this layer being less in refractivity than the microparticle layer. The conductive microparticle layer is such that a binder is permeated into gaps defined among neighboring microparticles, wherein the former is less in refractivity than the latter. This outside light absorption layer is expected to function also as an antistatic nonglare layer.
Still another principle of the color cathode ray tube of the invention is that the inside light absorption layer being formed on the inner panel surface is specifically arranged so that this layer is greater in thickness at the central part of a panel whereas the same layer is relatively thin at a peripheral portion thereof.
The panel of the color cathode ray tube of the invention is such that an equivalent radius of curvature as measured in an X direction stays identical in value at any locations along a Y direction while simultaneously letting an equivalent radius of curvature in the X direction be kept identical at any locations in the X direction. In addition, the equivalent radius of curvature of either an outer surface or inner face of the panel may also be substantially the same in value along the X and Y directions. Use of such panel curvature shape may suppress distortion of on-screen display images while improving implosion preventability of the cathode ray tube.
The panel of the color cathode ray tube of the invention is designed so that a relation of an outside equivalent radius of curvature Rxo and inside equivalent radius of curvature Rxi in the X direction with respect to the outer panel surface""s reference equivalent radius of curvature Rvo and the inner panel face""s reference equivalent radius of curvature Rvi is determined to satisfy Rxoxe2x89xa710Rvo and Rxixe2x89xa64Rvixe2x80x94preferably, Rxoxe2x89xa730Rvo and Rxixe2x89xa63Rvi.
The color cathode ray tube of the invention is such that when letting a main scanning direction on a display screen as formed in the panel be X direction while letting a specified direction at right angles to the main scan direction be Y direction, the panel""s inside equivalent radius of curvature Rxi in the X direction is greater than the inside equivalent radius of curvature Rxi by at least 2.6 times, preferably 5 times or above, more preferably 10 times or greater, wherein the tube has an inside light absorption layer on the inner panel surface. Further, said inside light absorption layer comprises pigment as its principal component, wherein a light absorption amount in luminous absorptivity of the inside light absorption layer at the center of said panel is designed to fall within a range of 10 to 60 percent (%), preferably 14 to 45%, more preferably 20-30%. Note here that the term xe2x80x9cluminous absorptivityxe2x80x9d (T) as used herein may be a specific value as defined by Equation (1) which follows:
T=(∫T(xcex)V(xcex)dxcex)/(∫V(xcex)dxcex)xe2x80x83xe2x80x83(1)
where T(xcex) is the absorption rate in a selected range of from 380 to 780 nanometers (nm) of wavelength (xcex), and V(xcex) is the relative luminous sensitivity in the wavelength range of 380 to 780 nm.
Additionally the light absorption amount as stated herein is to be understood to mean a value that is given by xe2x80x9c100-LT,xe2x80x9d where LT is the optical transmissivity (%).
With the color cathode ray tube of the invention, said transmissivity at the panel center may be greater than or equal to 70%, preferably 80% or more.
The color cathode ray tube of the invention is such that at least in the X direction of its panel, the equivalent radius of curvature Rxo of the outer panel surface is greater than the inside equivalent radius of curvature Rxi by 2.6 times or above, preferably 5 times or above, more preferably 10 times or more, wherein the tube has its inside light absorption layer overlying the inner panel surface and also has on said outer panel face an outside light absorption layer including an antireflective nonglare layer and antistatic layer, wherein said outside light absorption layer is greater in optical absorptivity at the panel center and yet is less at a peripheral portion of the panel, wherein said outside light absorption layer is comprised of a plurality of layers including at least one electrically insulative layer and more than one conductive layer, and wherein the conductive layer has its sheet resistance that is less in value at the panel center than at the periphery thereof.